Adjusting active cache size based on cache usage

ABSTRACT

Provided are a computer program product, system, and method for adjusting active cache size based on cache usage. An active cache in at least one memory device caches tracks in a storage during computer system operations. An inactive cache in the at least one memory device is not available to cache tracks in the storage during the computer system operations. During caching operations in the active cache, information is gathered on cache hits to the active cache and cache hits that would occur if the inactive cache was available to cache data during the computer system operations. The gathered information is used to determine whether to configure a portion of the inactive cache as part of the active cache for use during the computer system operations.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a computer program product, system, andmethod for adjusting active cache size based on cache usage.

2. Description of the Related Art

A cache management system buffers tracks in a storage device recentlyaccessed as a result of read and write operations in a faster accessstorage device, such as memory, than the storage device storing therequested tracks. Subsequent read requests to tracks in the fasteraccess cache memory are returned at a faster rate than returning therequested tracks from the slower access storage, thus reducing readlatency.

A cache management system may maintain a linked list having one entryfor each track stored in the cache, which may comprise write databuffered in cache before writing to the storage device or read data. Inthe commonly used Least Recently Used (LRU) cache technique, if a trackin the cache is accessed, i.e., a cache “hit”, then the entry in the LRUlist for the accessed track is moved to a Most Recently Used (MRU) endof the list. If the requested track is not in the cache, i.e., a cachemiss, then the track in the cache whose entry is at the LRU end of thelist may be removed (or destaged back to storage) and an entry for thetrack data staged into cache from the storage is added to the MRU end ofthe LRU list. With this LRU cache technique, tracks that are morefrequently accessed are likely to remain in cache, while data lessfrequently accessed will more likely be removed from the LRU end of thelist to make room in cache for newly accessed tracks.

There is a need for improved techniques for determining an amount ofcache to add to a computing system.

SUMMARY

Provided are a computer program product, system, and method foradjusting active cache size based on cache usage. An active cache in atleast one memory device caches tracks in a storage during computersystem operations. An inactive cache in the at least one memory deviceis not available to cache tracks in the storage during the computersystem operations. During caching operations in the active cache,information is gathered on cache hits to the active cache and cache hitsthat would occur if the inactive cache was available to cache dataduring the computer system operations. The gathered information is usedto determine whether to configure a portion of the inactive cache aspart of the active cache for use during the computer system operations.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an embodiment of a computing environment.

FIG. 2 illustrates an embodiment of a Least Recently Used (LRU) list.

FIG. 3 illustrates an embodiment of an active cache control block.

FIG. 4 illustrates an embodiment of an inactive cache control block.

FIG. 5 illustrates an embodiment of gathered cache access statistics.

FIG. 6 illustrates an embodiment of calculated cache access statistics.

FIG. 7 illustrates an embodiment of an operation to process a readrequest to a track.

FIG. 8 illustrates an embodiment of operations to calculate cache accessstatistics.

FIGS. 9, 10, and 11 illustrates embodiments of operations to expand theactive cache with the inactive cache.

FIG. 12 illustrates a computing environment in which the components ofFIG. 1 may be implemented.

DETAILED DESCRIPTION

When purchasing memory for computing systems, such as servers, users maynot fully anticipate the amount of cache workload that will occur in thesystem. Thus, users may not purchase enough cache at the time when theyinitially configure the system in order to reduce costs.

Described embodiments provide techniques to include in the systemadditional memory modules, but configure less than all the memory spaceas active cache available to the user for caching operations, leavingthe remainder of the memory inactive cache unavailable to cache data.During operations, information on cache usage may be gathered andprocessed to determine a cache service time of the average access timegiven the current amount of active cache and an estimation of anexpanded cache service time if the active cache was expanded with aportion of the inactive cache. This information may be used to determinewhether to use some of the inactive cache with the active cache toimprove cache performance.

FIG. 1 illustrates an embodiment of a computing environment. A computingsystem 100 accesses data in volumes 102 (e.g., Logical Unit Numbers,Logical Devices, Logical Subsystems, etc.) configured in a storage 104.The computing system 100 includes a processor 106 and a memory 108,including a cache 110 to cache data for the storage 104. The processor106 may comprise one or more central processing units (CPUs) or a groupof multiple cores on a single CPU. The cache 110 buffers data requestedby processes within the computing system. Alternatively, the computingsystem 100 may comprise a storage controller that processes Input/Output(I/O) access requests for tracks in the storage 104 from hosts 118connecting to the computing system 100 (storage controller) over anetwork 120.

The memory 108 further includes a storage manager 122 and cache manager124 The storage manager 122 manages access requests from internalprocesses in the computing system 100 and/or from hosts 118 for tracksin the storage 104. The cache manager 124 maintains accessed tracks inthe cache 110 for future read access to the track to allow the accessedtrack to be returned from the faster access cache 110 instead of thestorage 104. A track may comprise any unit of data configured in thestorage 104, such as a track, Logical Block Address (LBA), etc., whichis part of a larger grouping of tracks, such as a volume, logicaldevice, etc.

In one embodiment, the cache 110 may be partitioned into an active cache126 and an inactive cache 128, where the active cache 126 comprises thatportion of the physical memory 108 which is used to cache accessed data.The inactive cache 128 comprise that portion of the physical memory 108which is unavailable to the user and not used to cache user data, butmay be subsequently provisioned for use with the active cache asdescribed below. In this way, the memory vendor may sell the user morecache than the user initially needs, but provision a portion (all orpart) of the inactive cache 128 as part of the active cache 126 whenneeded. For instance, if the computing system 100 has a terabyte ofcache, the active cache 126 may be initially configured to be somepercentage of the total available cache, where the user is restrictedfrom using the inactive cache 128 during operations.

The cache manager 124 maintains cache management information 130 in thememory 108 to manage read (unmodified) and write (modified) tracks inthe active cache 126. The cache management information 130 may include atrack index 132 providing an index of tracks in the active cache 126 tocache control blocks in a control block directory 300; an active LeastRecently Used (LRU) list 200 _(A) for tracks in the active cache 126;and an inactive LRU list 200 _(IA) to indicate tracks that could havebeen stored in the inactive cache 128 portion had the inactive cache 128portion been available to store data. The cache control block directory300 includes the cache control blocks, where there is one cache controlblock for each track in the active cache 126 providing metadata on thetrack in the active cache 126. The track index 132 associates trackswith the cache control blocks providing information on the tracks in theactive cache 132. Upon determining that the active cache 200 _(A) isfull or has reached a threshold level, the LRU list 200 _(A) is used todetermine tracks to demote.

In one embodiment, there may only be cache control blocks 300 for theentries in the active cache 126 and no cache control blocks areallocated for tracks indicated in the inactive LRU list 200 _(IA). Atrack indicated in the inactive LRU list 200 _(IA) is not stored in theinactive cache 128. In an alternative embodiment, the cache controlblock directory 300 may maintain cache control blocks for tracksindicated in the inactive LRU list 200 _(IA) even though they are notstored in the cache 110. In one such embodiment using cache controlblocks for tracks indicated in the inactive LRU list 200 _(IA), thecache control blocks used for tracks in the inactive LRU list 200 _(IA)blocks, may be the same as those used for tracks in the active cache126, such as shown for FIG. 3, without information specific to the trackbeing maintained in the cache 110. In an alternative embodiment, thecache control block used for track in the inactive LRU list 200 _(IA)may have fewer fields and less information than those for tracksmaintained in the active cache 126, such as shown in FIG. 4. In suchembodiments, inactive cache control blocks for tracks in the inactiveLRU list 200 _(IA) may only maintain information about the inactive LRUlist 200 _(IA) where the tracks are indicated. For instance, for a trackin the active cache 126, a cache control block 300 _(i) may require 256bytes for a 4K block, but an inactive cache control block 400 _(i) for atrack only indicated in the inactive LRU list 200 _(IA) may onlycomprise 20 bytes.

During caching operations, the cache manager 124 may gather for specificperiods of time cache access statistics 500 on access to the activecache 126 and the inactive LRU list 200 _(IA). The cache manager 124 mayfurther calculate calculated cache access statistics 600, such as cacheservice times, for the currently used active cache 126 and ahypothetical expanded cache comprising a portion (some or all) of theinactive cache 128 configured for use with the active cache 126.

If based on the calculated cache service times for the active cache 126and an expanded cache, a determination is made to configure the inactivecache 128 for use with the active cache 126, then the cache manager 124may communicate with a cache service provider system 138 over thenetwork 120 to initiate a transaction to purchase the portion of theinactive cache 128 configured for use with the active cache 126.

With described embodiments, a vendor of memory devices, such as Dual InLine Memory Modules (DIMMs), may include more memory than a customerneeds and at some later time based on access usage provision some or allof the unused memory for use. The cache service provider 138 maymaintain user accounts 140 for users having inactive cache resources,and then the cache service provider 138 may initiate a financialtransaction to charge the user account 140 for the user of the computingsystem 100 for using the inactive cache 128. In this way, the memoryvendor may encourage users to increase their memory usage by determiningwhen more memory is needed to improve cache access times based on thegathered cache access statistics 500.

In the described embodiments, the lists 200 _(A) and 200 _(IA) compriseLRU lists. In alternative embodiments, the lists 200 _(A) and 200 _(IA)may comprise other types of lists to organize indication of tracks inthe cache 110.

The storage manager 122 and cache manager 124 are shown in FIG. 1 asprogram code loaded into the memory 108 and executed by the processor106. Alternatively, some or all of the functions may be implemented inhardware devices in the storage controller 104, such as in ApplicationSpecific Integrated Circuits (ASICs).

The storage 104 may comprise one or more storage devices known in theart, such as a solid state storage device (SSD) comprised of solid stateelectronics, EEPROM (Electrically Erasable Programmable Read-OnlyMemory), flash memory, flash disk, Random Access Memory (RAM) drive,storage-class memory (SCM), Phase Change Memory (PCM), resistive randomaccess memory (RRAM), spin transfer torque memory (STM-RAM), conductivebridging RAM (CBRAM), magnetic hard disk drive, optical disk, tape, etc.The storage devices may further be configured into an array of devices,such as Just a Bunch of Disks (JBOD), Direct Access Storage Device(DASD), Redundant Array of Independent Disks (RAID) array,virtualization device, etc. Further, the storage devices may compriseheterogeneous storage devices from different vendors or from the samevendor.

The memory 108 may comprise one or more a suitable volatile ornon-volatile memory devices, including those described above. The activecache 126 and inactive cache 128 may be configured in separate memorydevices, such as separate Dual In Line Memory Modules (DIMMs), or on thesame memory devices.

The network 120 may comprise a Storage Area Network (SAN), a Local AreaNetwork (LAN), a Wide Area Network (WAN), the Internet, and Intranet,etc.

FIG. 2 illustrates an embodiment of one of the LRU lists 200 _(i), suchas LRU lists 200 _(A) and 200 _(IA), as having a most recently used(MRU) end 202 identifying a track most recently added to the activecache 126 or most recently accessed in the cache 126 and a leastrecently used (LRU) end 204 from which the track identified at the LRUend 204 is selected to demote from the cache active cache 126. The LRUend 204 points to a track identifier, such as a track identifier addressor a cache control block index for the track, of the track that has beenin the active cache 126 the longest for tracks indicated in that list200 _(A). The inactive LRU list 200 _(IA) identifies tracks that couldhave been stored in the cache if the portion of the inactive cache 128was provisioned for use with the active cache 126.

FIG. 3 illustrates an embodiment of an active cache control block 300_(i) for one of the tracks in the active cache 126, including, but notlimited to, a cache control block identifier 302, such as an index valueof the cache control block 300 _(i); a track ID 304 of the track in thestorage 104; the active LRU list 306 in which the cache control block300 _(i) is indicated; an LRU list entry 308 at which the track isindicated; a cache timestamp 310 indicating a time the track was addedto the cache 116 and indicated on the LRU list 304; and additional trackmetadata 312 typically maintained for tracks stored in an active cache126.

FIG. 4 illustrates an embodiment of an inactive cache control block 400_(i) that may be maintained for a track indicated in the inactive LRUlist 200 _(IA), but not stored in the cache 110. The inactive cachecontrol block 400 _(i) includes fields 402, 404, 406, and 408 having thesame type of information in fields 302, 304, 306, 308, respectively, inthe active cache control block 300 _(i), but providing information onthe inactive LRU list 128 and entry in the inactive LRU list 128 entryfor the track. The cache control block directory 300 may include activeand inactive cache control blocks.

FIG. 5 illustrates an embodiment of gathered access statistics 500 thecache manager 124 gathers periodically during caching operations,including a number of active cache hits 502 comprising access requeststo tracks indicated in the active LRU list 200 _(A) in the active cache126; a number of inactive cache hits 504 comprising access requests totracks indicated in the inactive LRU list 200 _(IA) that are not in thecache 110; a number of read misses indicating a number of accessrequests to tracks not in the active cache 126; total time service cachehits 508 indicating a total accumulated time to service access requestswhen the track is in the active cache 126; and a total time to servicecache misses 510 indicating a total accumulated time to access requestedtracks not indicated in the active cache 126 from the storage 104 toreturn to a request.

FIG. 6 illustrates an embodiment of calculated cache access statistics600 calculated from the gathered access statistics 500, including acache hit rate 602 comprising the number of active cache hits 502divided by total cache accesses during the measured time period; aninactive cache hit rate 604 comprising the number of inactive cache hits504 divided by total cache accesses during the measured time period; acache hit service time 606 comprising the total time service cache hits508 divided by the number active cache hits 502; read miss service time608 comprising a total time service cache misses 510 divided by thenumber of read misses 506; an active cache service time 610 comprisingan average service time based on time to service cache hits and misseswhen only the active cache 126 is provisioned; and an estimated expandedcache service time 612 comprising a service time based on time toservice cache hits and misses if the portion of the inactive cache 128was configured for use with the active cache 126.

FIG. 7 illustrates an embodiment of operations performed by the cachemanager 124 to process a read request to a track in the storage 104.Upon receiving (at block 700) a read request to a track, if (at block702) the track is indicated in the active LRU list 200 _(A), then thetrack is returned (at block 704) to the request from the active cache126 and the number of active cache hits 502 is incremented (at block706). The total time to service cache hits 508 is incremented (at block708) by the time to return the requested track from the active cache126. Indication of the accessed track is moved (at block 710) to the MRUend 202 of the active LRU list 200 _(A).

If (at block 702) the track is not indicated in the active LRU list 200_(A), then the track is accessed (at block 712) from the storage 104 toreturn to the request. The cache manager 124 increments (at block 714)the number of read misses 506 and increments (at block 716) the totaltime service cache misses 510 by the time to return the track from thestorage 104. If (at block 718) the track is in the inactive LRU list 200_(IA), the cache manager 124 increments (at block 720) the number ofinactive cache hits 504 because if the inactive cache 128 was used,there would have been a cache hit. From block 720 or if the track is notin the inactive LRU list 200 _(IA), if (at block 722) the active LRUlist 200 _(A) is full, the track at the LRU end 204 of the active LRUlist 200 _(A) is demoted (at block 724) and discarded from the activecache 126.

If (at block 726) the inactive LRU list 200 _(IA) is full, then thecache manager 124 demotes (at block 728) indication of a track from theLRU end 204 of the inactive LRU list 200 _(IA). From block 728 or if theinactive LRU list 200 _(IA) is not full, then the cache manager 122 adds(at block 730) the track demoted from the LRU end 204 of the active LRUlist 200 _(A) to the MRU end 202 of the inactive LRU list 200 _(IA). Inthis way, the inactive LRU list 200 _(IA) provides a virtualrepresentation of the track as in cache, even though it is not in cache110, by indicating the track on the inactive LRU list 200 _(IA). Fromblock 730 or if the active LRU list 200 _(A) is not full (from block722), the cache manager 124 adds (at block 732) indication of theaccessed track to the MRU end 204 of the active LRU list 200 _(A) andadds the track to the active cache 126.

When adding a track to the active cache 126, the cache control block 300_(i) for that address in the active cache 126 would be updated toinclude information on the track and the entry in the active LRU list200 _(A) indicating the track. Further, the track index 132 would beupdated to include the cache control block index for the track in theactive cache 126. In one embodiment, if a track is indicated in theinactive LRU list 200 _(IA), there is no cache control block created forthe track and indicated in the cache control block directory 300. In analternative embodiment, a full cache control block 300 _(i) may becreated in the cache control block directory 300 for the track indicatedin the inactive LRU list 200 _(IA). In a still further alternativeembodiment, a smaller inactive cache control block 400 _(i) may be addedto the cache control block directory 300 for the track indicated in theinactive LRU list 200 _(IA) having minimal information to identify thetrack in the inactive LRU list 200 _(IA). The cache control block indexfor the inactive cache control block 400 _(i) may be added to the trackindex 132 for the track indicated in the inactive LRU list 200 _(IA).

With the described embodiments of FIG. 7, tracks demoted from the activeLRU list 200 _(A) and removed from the cache 110 are added to theinactive LRU list 200 _(IA) where accesses to the track once removedfrom the cache 110 can be tracked as if the track is in the cache 110.These accesses to the track indicated on the inactive LRU list 200 _(IA)can be used to estimate the cache performance that would be realized ifthe inactive cache 128 was configured to be part of the active cache 126and available for caching tracks.

FIG. 8 illustrates an embodiment of operations performed by the cachemanager 124 (or some other component) to periodically initiateoperations to gather and analyze cache access statistics. Uponinitiating (at block 800) such operations, the cache manager 124calculates (at block 802) the active cache hit rate 602 as the numberactive cache hits 502 divided by the total cache hits during themeasurement time period. The inactive cache hit rate 604 is calculated(at block 804) as the number inactive cache hits 504 divided by thetotal cache hits during the measurement time period. The cache manager124 calculates (at block 806) the read miss service time 608 as thetotal time service cache misses 510 divided by the total read misses506. The cache hit service time 606 is calculated (at block 808) as thetotal time service cache hits 508 divided by the total active cache hits502.

The cache manager 124 may then calculate (at block 810) the active cacheservice time 610 as follows:

(active cache hit rate 602*cache hit service time 606)+read miss servicetime 608*(1−active cache hit rate 602)

The cache manager 124 may then calculate (at block 812) the estimatedexpanded cache service time 612 when the inactive cache 128 is presumedto have been used as:

((active cache hit rate 602+inactive cache hit rate 604)*cache hitservice time 606)+read miss service time 608*(1−(active cache hit rate602+inactive cache hit rate 604)).

The calculated active cache service time 610 and the estimated expandedcache service time 612 are returned (at block 814). The active cacheservice time 610 indicates an average time to service requests when onlythe active cache 126 is used. The estimated expanded cache service time612 indicates an estimated time to service requests if both the activecache 126 and a portion of the inactive cache 128 are used. Afterperforming all calculations, the gathered access statistics 500 arereset (at block 816).

FIG. 9 illustrates an embodiment of operations performed by the cachemanager 124 (or some other component in the computing system 100) to usethe returned active cache service time 610 and the estimated expandedcache service time 612 to determine whether to activate some of theinactive cache 128 to improve cache performance to approximate theestimated expanded cache service time 612. Upon initiating (at block900) operations to expand the active cache 126, the cache manager 124determines (at block 902) whether the estimated expanded cache servicetime 612 exceeds the active cache service time 610 by a predeterminedratio, e.g., 50% more. If so, then the cache manager 124 presents (atblock 904) a request to the user of the computing system 100, such asthrough a notification in the display screen, to expand the active cache126. The request may indicate the potential improvement based on theexpanded cache service time 612 as compared to the active cache servicetime 610, may indicate a cost of adding a portion of the inactive cache128, and may include a graphical button the user may select to expandthe active cache 126. If (at block 906) the user accepts the request toexpand the active cache 126, then the cache manager 124 configures (atblock 908) a portion (some or all) of the inactive cache 128 as part ofthe active cache 126. The cache manager 124 may transmit (at block 910)a message to the cache service provider 138 to initiate a transaction topurchase the additional inactive cache 128 added to the active cache126, which may be charged to the user account 140. The charges maycomprise periodic charges for certain time intervals during which theportion of the inactive cache 128 is added to the active cache 126. Ifthe predetermined ratio is not exceeded (from the no branch of block902) or the user does not accept the request to expand the active cache(at block 906) control ends without provisioning some of the inactivecached 128 to the active cache 126.

FIG. 10 illustrates an alternative embodiment of operations performed bythe cache manager 124 (or some other component in the computing system100) to use the returned active cache service time 610 and the estimatedexpanded cache service time 612 to determine whether to expand or reducethe active cache 126 size. Upon initiating (at block 1000) suchoperations, if (at block 1002) the active cache 126 has not already beenexpanded to include a portion of the inactive cache 128, the cachemanager 124 determines (at block 1004) whether the estimated expandedcache service time 612 exceeds the active cache service time 610 by afirst predetermined ratio, e.g., 50% more. If so, then the cache manager124 configures (at block 1006) a portion (some or all) of the inactivecache 128 as part of the active cache 126. The cache manager 124 maytransmit (at block 1008) a message to the cache service provider 138 toinitiate a transaction to purchase the additional inactive cache 128added to the active cache 126, which may be charged to the user account140. The charges may comprise periodic charges for certain timeintervals during which the portion of the inactive cache 128 is added tothe active cache 126. If (at block 1004) the first predetermined ratiois not exceeded, then control ends.

If (at block 1002) the active cache 126 has already been expanded toinclude a portion of the inactive cache 128, then the cache manager 124determines (at block 1010) whether the active cache service time (withthe expanded cache) not exceed an initial active cache service time by asecond predetermined ratio, which may be less than the firstpredetermined ratio. After the cache has been expanded, the cachemanager may maintain statistics to determine the actual expanded cacheservice time and an estimated cache service time if the cache was notexpanded. If (at block 1010) the expanded active cache is not exceedinghow the cache would perform with just the active cache 126 by asufficient ratio, then the cache manager 124 configures (at block 1012)the active cache 126 to remove from the active cache the portion of theinactive cache 128 previously configured as part of the active cache126. The cache manager 124 may transmit (at block 1014) a message to thecache service provider 138 to purchase additional cache for a durationduring which the inactive cache 128 was configured to be part of theactive cache 126. If (at block 1010) the second predetermined ratio isexceeded, then control ends.

FIG. 11 illustrates a yet further embodiment for how the inactive cache128 may be provisioned for use. Upon detecting (at block 1100) a failureof one of the memory modules, e.g., DIMMs, used for the active cache126, then the cache manager 124 may configure (at block 1102) one of thememory modules in which the inactive cache 128 is implemented to usewith the active cache 126 to replace the failed memory module. The cachemanager 124 may then transmit a message to the cache service provider128 to initiate a transaction to purchase on behalf of the user account140 for the computing system 100 the additional inactive cache 138 addedto the active cache 126 to replace a failed memory module.

In the embodiments of FIGS. 9, 10, and 11, when configuring the inactivecache 128 to add to the active cache 126, the cache manager 124 may needto add cache control blocks 300 _(i) (FIG. 3) to the cache control blockdirectory 300 for the tracks added from the inactive cache 128 to theactive cache 126, as well as add entries to the active LRU list 200 _(A)for the added portions of the inactive cache 128. In embodiments, wherethe cache control block directory 300 includes the shortened inactivecache control blocks 400 _(i) for inactive cache 128 entries, the cachemanager 124 would convert the inactive cache control blocks 400 i tofull active cache control blocks 300 _(i) for tracks entries in theinactive cache 128 added to the active cache 126.

In the described embodiment, the variable “i” when used with differentelements may denote a same or different instance of that element.

With the described embodiments, the vendor may include additional memoryin the memory device that is used as active cache. Then duringoperations the system may assign a portion of the inactive cache to usewith the active cache if gathered usage statistics indicate theperformance benefits of adding the inactive cache would significantlyimprove performance. At this time, the user may be charged for theadditional cache resources allocated as active cache. With the describedembodiments, a user may easily expand their cache size based on cacheusage.

The present invention may be a system, a method, and/or a computerprogram product. The computer program product may include a computerreadable storage medium (or media) having computer readable programinstructions thereon for causing a processor to carry out aspects of thepresent invention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Java, Smalltalk, C++ or the like,and conventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

The computational components of FIG. 1, including the hosts 118, cacheservice provider 138, and computing system 100 may be implemented in oneor more computer systems, such as the computer system 1202 shown in FIG.12. Computer system/server 1202 may be described in the general contextof computer system executable instructions, such as program modules,being executed by a computer system. Generally, program modules mayinclude routines, programs, objects, components, logic, data structures,and so on that perform particular tasks or implement particular abstractdata types. Computer system/server 1202 may be practiced in distributedcloud computing environments where tasks are performed by remoteprocessing devices that are linked through a communications network. Ina distributed cloud computing environment, program modules may belocated in both local and remote computer system storage media includingmemory storage devices.

As shown in FIG. 12, the computer system/server 1202 is shown in theform of a general-purpose computing device. The components of computersystem/server 1202 may include, but are not limited to, one or moreprocessors or processing units 1204, a system memory 1206, and a bus1208 that couples various system components including system memory 1206to processor 1204. Bus 1208 represents one or more of any of severaltypes of bus structures, including a memory bus or memory controller, aperipheral bus, an accelerated graphics port, and a processor or localbus using any of a variety of bus architectures. By way of example, andnot limitation, such architectures include Industry StandardArchitecture (ISA) bus, Micro Channel Architecture (MCA) bus, EnhancedISA (EISA) bus, Video Electronics Standards Association (VESA) localbus, and Peripheral Component Interconnects (PCI) bus.

Computer system/server 1202 typically includes a variety of computersystem readable media. Such media may be any available media that isaccessible by computer system/server 1202, and it includes both volatileand non-volatile media, removable and non-removable media.

System memory 1206 can include computer system readable media in theform of volatile memory, such as random access memory (RAM) 1210 and/orcache memory 1212. Computer system/server 1202 may further include otherremovable/non-removable, volatile/non-volatile computer system storagemedia. By way of example only, storage system 1213 can be provided forreading from and writing to a non-removable, non-volatile magnetic media(not shown and typically called a “hard drive”). Although not shown, amagnetic disk drive for reading from and writing to a removable,non-volatile magnetic disk (e.g., a “floppy disk”), and an optical diskdrive for reading from or writing to a removable, non-volatile opticaldisk such as a CD-ROM, DVD-ROM or other optical media can be provided.In such instances, each can be connected to bus 1208 by one or more datamedia interfaces. As will be further depicted and described below,memory 1206 may include at least one program product having a set (e.g.,at least one) of program modules that are configured to carry out thefunctions of embodiments of the invention.

Program/utility 1214, having a set (at least one) of program modules1216, may be stored in memory 1206 by way of example, and notlimitation, as well as an operating system, one or more applicationprograms, other program modules, and program data. Each of the operatingsystem, one or more application programs, other program modules, andprogram data or some combination thereof, may include an implementationof a networking environment. The components of the computer 1202 may beimplemented as program modules 1216 which generally carry out thefunctions and/or methodologies of embodiments of the invention asdescribed herein. The systems of FIG. 1 may be implemented in one ormore computer systems 1202, where if they are implemented in multiplecomputer systems 1202, then the computer systems may communicate over anetwork.

Computer system/server 1202 may also communicate with one or moreexternal devices 1218 such as a keyboard, a pointing device, a display1220, etc.; one or more devices that enable a user to interact withcomputer system/server 1202; and/or any devices (e.g., network card,modem, etc.) that enable computer system/server 1202 to communicate withone or more other computing devices. Such communication can occur viaInput/Output (I/O) interfaces 1222. Still yet, computer system/server1202 can communicate with one or more networks such as a local areanetwork (LAN), a general wide area network (WAN), and/or a publicnetwork (e.g., the Internet) via network adapter 1224. As depicted,network adapter 1224 communicates with the other components of computersystem/server 1202 via bus 1208. It should be understood that althoughnot shown, other hardware and/or software components could be used inconjunction with computer system/server 1202. Examples, include, but arenot limited to: microcode, device drivers, redundant processing units,external disk drive arrays, RAID systems, tape drives, and data archivalstorage systems, etc.

The terms “an embodiment”, “embodiment”, “embodiments”, “theembodiment”, “the embodiments”, “one or more embodiments”, “someembodiments”, and “one embodiment” mean “one or more (but not all)embodiments of the present invention(s)” unless expressly specifiedotherwise.

The terms “including”, “comprising”, “having” and variations thereofmean “including but not limited to”, unless expressly specifiedotherwise.

The enumerated listing of items does not imply that any or all of theitems are mutually exclusive, unless expressly specified otherwise.

The terms “a”, “an” and “the” mean “one or more”, unless expresslyspecified otherwise.

Devices that are in communication with each other need not be incontinuous communication with each other, unless expressly specifiedotherwise. In addition, devices that are in communication with eachother may communicate directly or indirectly through one or moreintermediaries.

A description of an embodiment with several components in communicationwith each other does not imply that all such components are required. Onthe contrary a variety of optional components are described toillustrate the wide variety of possible embodiments of the presentinvention.

When a single device or article is described herein, it will be readilyapparent that more than one device/article (whether or not theycooperate) may be used in place of a single device/article. Similarly,where more than one device or article is described herein (whether ornot they cooperate), it will be readily apparent that a singledevice/article may be used in place of the more than one device orarticle or a different number of devices/articles may be used instead ofthe shown number of devices or programs. The functionality and/or thefeatures of a device may be alternatively embodied by one or more otherdevices which are not explicitly described as having suchfunctionality/features. Thus, other embodiments of the present inventionneed not include the device itself.

The foregoing description of various embodiments of the invention hasbeen presented for the purposes of illustration and description. It isnot intended to be exhaustive or to limit the invention to the preciseform disclosed. Many modifications and variations are possible in lightof the above teaching. It is intended that the scope of the invention belimited not by this detailed description, but rather by the claimsappended hereto. The above specification, examples and data provide acomplete description of the manufacture and use of the composition ofthe invention. Since many embodiments of the invention can be madewithout departing from the spirit and scope of the invention, theinvention resides in the claims herein after appended.

1-24. (canceled)
 25. A computer program product for managing cache in atleast one memory device in a computer system to cache tracks stored in astorage, the computer program product comprising a computer readablestorage medium having computer readable program code embodied thereinthat when executed performs operations, the operations comprising:maintaining an active cache list indicating tracks in an active cachecomprising a first portion of the at least one memory device to cachethe tracks in the storage during computer system operations; maintainingan inactive cache list indicating tracks demoted from the active cache;during caching operations, gathering information on active cache hitscomprising access requests to tracks indicated in the active cache listand inactive cache hits comprising access requests to tracks indicatedin the inactive cache list; and using the gathered information todetermine whether to provision a second portion of the at least onememory device unavailable to cache user data to be part of the activecache for use to cache user data during the computer system operations.26. The computer program product of claim 25, wherein the operationsfurther comprise: providing an active Least Recently Used (LRU) list inwhich tracks included in the active cache are indicated, wherein theinactive cache list comprises an inactive LRU list.
 27. The computerprogram product of claim 25, wherein the operations further comprise:staging a track requested by an access request indicated in the inactivecache list from the storage to the active cache; and adding indicationof the staged track to the active cache list.
 28. The computer programproduct of claim 27, wherein the operations further comprise: inresponse determining that the active cache list is full: demoting atrack from the active cache list to include the staged track;determining whether the inactive cache list is full; and demoting atrack from the inactive cache list in response to determining that theinactive cache list is full; and adding the track demoted from theactive cache list to the inactive cache list.
 29. The computer programproduct of claim 25, wherein tracks indicated in the inactive cache listare not stored in the at least one memory device.
 30. The computerprogram product of claim 25, wherein the using the gathered informationcomprises: determining an active cache service time based on a number ofthe active cache hits; determining an expanded cache service time basedon the number of the active cache hits and a number of the inactivecache hits; and comparing the determined active cache service time andthe expanded cache service time to determine whether to provision thesecond portion of the at least one memory device to be part of theactive cache.
 31. The computer program product of claim 25, wherein theat least one memory device is comprised of a plurality of memorymodules, wherein the operations further comprise: detecting a failure ofone of the memory modules implementing of with the active cache; andprovisioning one of the memory modules unavailable to cache user data tobe part of the active cache in response to determining the failure ofone of the memory modules used with the active cache to replace thefailed memory module.
 32. A system coupled to a storage having tracks,comprising: a processor; at least one memory device; a computer readablestorage medium having computer program code that in response to beingexecuted by the processor performs operations, the operationscomprising: maintaining an active cache list indicating tracks in anactive cache comprising a first portion of the at least one memorydevice to cache the tracks in the storage during computer systemoperations; maintaining an inactive cache list indicating tracks demotedfrom the active cache; during caching operations, gathering informationon active cache hits comprising access requests to tracks indicated inthe active cache list and inactive cache hits comprising access requeststo tracks indicated in the inactive cache list; and using the gatheredinformation to determine whether to provision a second portion of the atleast one memory device unavailable to cache user data to be part of theactive cache for use to cache user data during the computer systemoperations.
 33. The system of claim 32, wherein the operations furthercomprise: providing an active Least Recently Used (LRU) list in whichtracks included in the active cache are indicated, wherein the inactivecache list comprises an inactive LRU list.
 34. The system of claim 32,wherein the operations further comprise: staging a track requested by anaccess request indicated in the inactive cache list from the storage tothe active cache; and adding indication of the staged track to theactive cache list.
 35. The system of claim 34, wherein the operationsfurther comprise: in response determining that the active cache list isfull: demoting a track from the active cache list to include the stagedtrack; determining whether the inactive cache list is full; and demotinga track from the inactive cache list in response to determining that theinactive cache list is full; and adding the track demoted from theactive cache list to the inactive cache list.
 36. The system of claim32, wherein tracks indicated in the inactive cache list are not storedin the at least one memory device.
 37. The system of claim 32, whereinthe using the gathered information comprises: determining an activecache service time based on a number of the active cache hits;determining an expanded cache service time based on the number of theactive cache hits and a number of the inactive cache hits; and comparingthe determined active cache service time and the expanded cache servicetime to determine whether to provision the second portion of the atleast one memory device to be part of the active cache.
 38. The systemof claim 32, wherein the at least one memory device is comprised of aplurality of memory modules, wherein the operations further comprise:detecting a failure of one of the memory modules implementing of withthe active cache; and provisioning one of the memory modules unavailableto cache user data to be part of the active cache in response todetermining the failure of one of the memory modules used with theactive cache to replace the failed memory module.
 39. A method formanaging a cache provisioned in at least one memory device in a computersystem to cache tracks stored in a storage, comprising: maintaining anactive cache list indicating tracks in an active cache comprising afirst portion of the at least one memory device to cache the tracks inthe storage during computer system operations; maintaining an inactivecache list indicating tracks demoted from the active cache; duringcaching operations, gathering information on active cache hitscomprising access requests to tracks indicated in the active cache listand inactive cache hits comprising access requests to tracks indicatedin the inactive cache list; and using the gathered information todetermine whether to provision a second portion of the at least onememory device unavailable to cache user data to be part of the activecache for use to cache user data during the computer system operations.40. The method of claim 39, further comprising: providing an activeLeast Recently Used (LRU) list in which tracks included in the activecache are indicated, wherein the inactive cache list comprises aninactive LRU list.
 41. The method of claim 39, further comprising:staging a track requested by an access request indicated in the inactivecache list from the storage to the active cache; and adding indicationof the staged track to the active cache list.
 42. The method of claim41, further comprising: in response determining that the active cachelist is full: demoting a track from the active cache list to include thestaged track; determining whether the inactive cache list is full; anddemoting a track from the inactive cache list in response to determiningthat the inactive cache list is full; and adding the track demoted fromthe active cache list to the inactive cache list.
 43. The method ofclaim 39, wherein tracks indicated in the inactive cache list are notstored in the at least one memory device.
 44. The method of claim 39,wherein the using the gathered information comprises: determining anactive cache service time based on a number of the active cache hits;determining an expanded cache service time based on the number of theactive cache hits and a number of the inactive cache hits; and comparingthe determined active cache service time and the expanded cache servicetime to determine whether to provision the second portion of the atleast one memory device to be part of the active cache.